/**********************************************************************
 *
 * Filename:    memtest.c
 *
 * Description: General-purpose memory testing functions.
 *
 * Notes:       This software can be easily ported to systems with
 *              different data bus widths by redefining 'datum'.
 *
 *
 * Copyright (c) 1998 by Michael Barr.  This software is placed into
 * the public domain and may be used for any purpose.  However, this
 * notice must not be changed or removed and no warranty is either
 * expressed or implied by its publication or distribution.
 **********************************************************************/


#include "memtest.h"


/**********************************************************************
 *
 * Function:    memTestDataBus()
 *
 * Description: Test the data bus wiring in a memory region by
 *              performing a walking 1's test at a fixed address
 *              within that region.  The address (and hence the
 *              memory region) is selected by the caller.
 *
 * Notes:
 *
 * Returns:     0 if the test succeeds.
 *              A non-zero result is the first pattern that failed.
 *
 **********************************************************************/
datum
memTestDataBus(volatile datum *address)
{
    datum pattern;
    /*
     * Perform a walking 1's test at the given address.
     */
    for (pattern = 1; pattern != 0; pattern <<= 1) {
        /*
         * Write the test pattern.
         */
        *address = pattern;
        /*
         * Read it back (immediately is okay for this test).
         */
        if (*address != pattern) {
            return (pattern);
        }
    }
    return (0);
}   /* memTestDataBus() */


/**********************************************************************
 *
 * Function:    memTestAddressBus()
 *
 * Description: Test the address bus wiring in a memory region by
 *              performing a walking 1's test on the relevant bits
 *              of the address and checking for aliasing. This test
 *              will find single-bit address failures such as stuck
 *              -high, stuck-low, and shorted pins.  The base address
 *              and size of the region are selected by the caller.
 *
 * Notes:       For best results, the selected base address should
 *              have enough LSB 0's to guarantee single address bit
 *              changes.  For example, to test a 64-Kbyte region,
 *              select a base address on a 64-Kbyte boundary.  Also,
 *              select the region size as a power-of-two--if at all
 *              possible.
 *
 * Returns:     NULL if the test succeeds.
 *              A non-zero result is the first address at which an
 *              aliasing problem was uncovered.  By examining the
 *              contents of memory, it may be possible to gather
 *              additional information about the problem.
 *
 **********************************************************************/
datum *
memTestAddressBus(volatile datum *baseAddress, uint32_t nBytes)
{
    uint32_t addressMask = (nBytes / sizeof(datum) - 1);
    uint32_t offset;
    uint32_t testOffset;
    datum pattern     = (datum) 0xAAAAAAAA;
    datum antipattern = (datum) 0x55555555;
    /*
     * Write the default pattern at each of the power-of-two offsets.
     */
    for (offset = 1; (offset & addressMask) != 0; offset <<= 1) {
        baseAddress[offset] = pattern;
    }
    /*
     * Check for address bits stuck high.
     */
    testOffset = 0;
    baseAddress[testOffset] = antipattern;
    for (offset = 1; (offset & addressMask) != 0; offset <<= 1) {
        if (baseAddress[offset] != pattern) {
            return ((datum *) &baseAddress[offset]);
        }
    }
    baseAddress[testOffset] = pattern;
    /*
     * Check for address bits stuck low or shorted.
     */
    for (testOffset = 1; (testOffset & addressMask) != 0; testOffset <<= 1) {
        baseAddress[testOffset] = antipattern;
        if (baseAddress[0] != pattern) {
            return ((datum *) &baseAddress[testOffset]);
        }
        for (offset = 1; (offset & addressMask) != 0; offset <<= 1) {
            if ((baseAddress[offset] != pattern) && (offset != testOffset)) {
                return ((datum *) &baseAddress[testOffset]);
            }
        }
        baseAddress[testOffset] = pattern;
    }
    return (NULL);
}   /* memTestAddressBus() */


/**********************************************************************
 *
 * Function:    memTestDevice()
 *
 * Description: Test the integrity of a physical memory device by
 *              performing an increment/decrement test over the
 *              entire region.  In the process every storage bit
 *              in the device is tested as a zero and a one.  The
 *              base address and the size of the region are
 *              selected by the caller.
 *
 * Notes:
 *
 * Returns:     NULL if the test succeeds.
 *
 *              A non-zero result is the first address at which an
 *              incorrect value was read back.  By examining the
 *              contents of memory, it may be possible to gather
 *              additional information about the problem.
 *
 **********************************************************************/
datum *
memTestDevice(volatile datum *baseAddress, uint32_t nBytes)
{
    uint32_t offset;
    uint32_t nWords = nBytes / sizeof(datum);
    datum pattern;
    datum antipattern;
    /*
     * Fill memory with a known pattern.
     */
    for (pattern = 1, offset = 0; offset < nWords; pattern++, offset++) {
        baseAddress[offset] = pattern;
    }
    /*
     * Check each location and invert it for the second pass.
     */
    for (pattern = 1, offset = 0; offset < nWords; pattern++, offset++) {
        if (baseAddress[offset] != pattern) {
            return ((datum *) &baseAddress[offset]);
        }
        antipattern = ~pattern;
        baseAddress[offset] = antipattern;
    }
    /*
     * Check each location for the inverted pattern and zero it.
     */
    for (pattern = 1, offset = 0; offset < nWords; pattern++, offset++) {
        antipattern = ~pattern;
        if (baseAddress[offset] != antipattern) {
            return ((datum *) &baseAddress[offset]);
        }
    }
    return (NULL);
}   /* memTestDevice() */
